Mammalian galanin receptors

ABSTRACT

The present invention provides isolated mammalian GalR3 receptors, isolated or recombinant nucleic acids and recombinant vectors encoding the same, host cells comprising the nucleic acids and vectors, and methods for making the receptors using the host cells. This invention further provides antibodies and antigen binding fragments thereof which specifically bind to the receptors and are useful for treating medical conditions caused or mediated by galanin. Also provided are screening methods for identifying specific agonists and antagonists of the mammalian GalR3 receptors.

This application is a continuation of U.S. patent application Ser. No.11/768,449, filed Jun. 26, 2007, which is a continuation of U.S. patentapplication Ser. No. 10/946,767, filed Sep. 22, 2004, now U.S. Pat. No.7,250,163; which is a continuation of U.S. patent application Ser. No.10/779,021, filed Feb. 13, 2004 which is a divisional of U.S. patentapplication Ser. No. 08/916,247, filed Aug. 22, 1997, now U.S. Pat. No.6,693,182; each of which is herein incorporated by reference in itsentirety.

TECHNICAL FIELD

The present invention relates to mammalian galanin receptors. Moreparticularly, it relates to rat and human galanin receptors, isolatednucleic acids and recombinant vectors encoding the receptors, methodsfor making the receptors, fragments or fusion proteins thereof usingrecombinant DNA methodology or chemical synthesis, and to methods forusing the receptors in screening systems to identify inhibitors for thetreatment of various diseases. This invention further relates toantibodies, both polyclonal and monoclonal, which specifically bind tothe galanin receptors or to anti-idiotypic antibodies against them, andto fragments and fusion proteins thereof.

BACKGROUND OF THE INVENTION

Galanin is a polypeptide found in the central and peripheral nervoussystems which regulates multiple processes such as endocrine andexocrine pancreatic secretions, intestinal motility, and modulation ofbehavioral, cognitive, and sensory functions such as feeding, learning,memory and nociception. See, e.g., Merchenthaler et al., Prog.Neurobiol. 40:711-769 (1993), and Hökfelt et al. in Galanin: A NewMultifunctional Peptide in the Neuro-Endocrine System, Wenner-GrenInternational Symposium Series, 1991, Vol. 58, MacMillan, Cambridge,U.K. Because of its wide distribution and multiple activities, Galaninis believed to be involved in a number of medical conditions, includingobesity, Alzheimer's disease, nociception, dementia, eating disorders,diabetes, dislipoproteinemia, developmental disorders of the neuralsystems, disorders of the digestive systems, growth disorders, sexualand reproductive dysfunctions, stomach ulcers, sleep disorders, andregeneration of injured neuronal systems.

The physiological effects of galanin are mediated by specific receptorsin target tissues. One such receptor from insulin-secreting cells hasbeen described by Lagny-Pourmir et al. [Endocrinology 124:2635-2641(1989)]. Human galanin receptors have been cloned by Habert-Ortoli etal. [Proc. Natl. Acad. Sci. USA 91:9780-9783 (1994)], Hinuma et al.[European Patent Application Publication EP 0 711 830 A2] and Amiranoffet al. [International Patent Application Publication No. WO 95/22608].

In view of the important role of galanin in many physiological processesand medical conditions, there is a need for materials and methods foridentifying selective agonists and antagonists of galanin.

SUMMARY OF THE INVENTION

The present invention fills the foregoing need by providing suchmaterials and methods. More particularly, this invention provides novelmammalian galanin receptors, isolated or recombinant nucleic acidsencoding the receptors, and recombinant vectors and host cellscomprising such nucleic acids.

The isolated or recombinant nucleic acids are selected from the groupconsisting of:

(a) a nucleic acid encoding a mammalian galanin receptor comprising anamino acid sequence defined by SEQ ID NO: 2 or SEQ ID NO: 4, or asubsequence thereof;

(b) a nucleic acid that hybridizes under moderately stringent conditionsto the nucleic acid of (a) and encodes a polypeptide that (i) bindsgalanin and (ii) is at least 80% identical to a receptor encoded by thenucleic acid of (a); and

(c) a nucleic acid that, due to the degeneracy of the genetic code,encodes a mammalian galanin receptor encoded by a nucleic acid of (a) or(b).

This invention further provides methods for making the galanin receptorscomprising culturing a host cell comprising a nucleic acid encoding amammalian galanin receptor comprising an amino acid sequence defined bySEQ ID NO: 2 or SEQ ID NO: 4, or a subsequence thereof, under conditionsin which the nucleic acid is expressed. In some embodiments, the methodfurther comprises isolation of the receptor from the culture.

This invention also provides polypeptides comprising a fragment of amammalian galanin receptor having an amino acid sequence correspondingto the sequence of at least about 8 contiguous residues of the completereceptor sequence. Preferably, the polypeptides comprise at least about12, more preferably at least about 20, and most preferably at leastabout 30 such residues.

Still further, this invention provides fusion proteins comprising amammalian galanin receptor or a polypeptide therefrom covalently linkedto a fusion partner.

The present invention also provides antibodies, both polyclonal andmonoclonal, that specifically bind to one or more of the galaninreceptors or to polypeptides therefrom, and anti-idiotypic antibodies,both monoclonal and polyclonal, which specifically bind to the foregoingantibodies.

This invention further provides a method for producing a mammaliangalanin receptor comprising culturing a host cell comprising a nucleicacid encoding a mammalian galanin receptor comprising an amino acidsequence defined by SEQ ID NO: 2 or SEQ ID NO: 4, or a subsequencethereof, under conditions in which the nucleic acid is expressed. In oneembodiment the receptor is isolated from the culture.

This invention still further provides a method for treatinggalanin-mediated medical conditions comprising administering to a mammalafflicted with a medical condition caused or mediated by galanin, aneffective amount of an antibody, or an antigen-binding fragment thereof,that specifically binds to a mammalian galanin receptor having an aminoacid sequence defined by SEQ ID NO: 4, or a subsequence thereof, andpharmaceutical compositions comprising one or more of such antibodies orfragments and a pharmaceutically acceptable carrier. Preferably, themammal is a human being.

The present invention also provides a method for identifying a galaninagonist or antagonist comprising:

-   -   (a) contacting a mammalian galanin receptor having an amino acid        sequence defined by SEQ ID NO: 2 or SEQ ID NO: 4, or a        subsequence thereof, in the presence of a known amount of        labeled galanin with a sample to be tested for the presence of a        galanin agonist or antagonist; and    -   (b) measuring the amount of labeled galanin specifically bound        to the receptor;        whereby a galanin agonist or antagonist in the sample is        identified by measuring substantially reduced binding of the        labeled galanin to the galanin receptor, compared to what would        be measured in the absence of such agonist or antagonist.

In a preferred embodiment, membranes isolated from mammalian cellscomprising a nucleic acid encoding the galanin receptor are used as thesource of the receptor.

BRIEF DESCRIPTION OF THE FIGURES

The present invention can be more readily understood by reference to thefollowing Description and Examples, and to the accompanying Figures, inwhich:

FIG. 1 is a graphical representation of the specific binding of¹²⁵I-galanin to cellular receptors, showing bound radioactivity as afunction of ligand concentration; and

FIG. 2 is a graphical representation of the inhibition of the binding of¹²⁵I-porcine galanin to cellular receptors by various known galaninagonists and antagonists, showing percent inhibition of radioligandbinding as a function of ligand concentration. The competing ligandswere rat galanin (), chimeric galanin peptide C7 (◯), galanin(2-29)(□), galanin(3-29) (•) and galanin(10-20) (▴).

DESCRIPTION OF THE INVENTION

All references cited herein are hereby incorporated herein in theirentirety by reference.

As used herein, the term “ligand” is defined to mean any moleculecapable of specifically binding to the mammalian galanin receptors ofthe invention. Thus galanin itself is a ligand, as are agonists andantagonists that may compete with galanin for specific binding to thereceptors.

Galanin Receptor Characterization

As has been noted above, others had identified galanin receptors fromvarious species and tissues prior to the present invention. Thus, thereappears to be a family of galanin receptor subtypes. The human receptorcloned by Habert-Ortoli et al., supra, was the first and hence has beencalled the type 1 galanin receptor (GalR1). Homologous GalR1 receptorshave been cloned from rat Rin14B insulinoma cells [Parker et al., Mol.Brain Res. 34:179-189 (1995)] and from rat brain [Burgevin et al., J.Mol. Neurosci. 6:33-41 (1995)].

More recently a second galanin receptor subtype, type 2 (GalR2), hasbeen described in rat by Howard et al. [FEBS Lett. 405:285-290 (1997)and by Wang et al. [Mol. Pharmacol. Vol. 52:1 (1997) (in press)].Because of the previously known existence of type 1 and type 2 galaninreceptors, the novel galanin receptors of this invention may be referredto as type 3 galanin receptors (GalR3).

The nucleotide sequence of the complete open reading frame and thecorresponding amino acid sequence of rat GalR3 receptor cDNA are definedin the Sequence Listing by SEQ ID NO: 1 and SEQ ID NO: 2, respectively.The nucleotide sequence of the complete open reading frame and thecorresponding amino acid sequence of the human GalR3 receptor aredefined in the Sequence Listing by SEQ ID NO: 3 and SEQ ID NO: 4,respectively.

In comparing the complete rat and human cDNA sequences, it has beenfound that the human sequence is longer, and that a region encoded bybases 169 to 1275 (amino acid residues 61-424) of the complete humansequence is highly homologous to the rat sequence. The human GalR3receptor sequence may thus be regarded as having two forms—a “long” formencompassing the entire sequence defined by SEQ ID NO: 4, and a “short”form encompassing the region encoded by bases 169 to 1275 of SEQ ID NO:3.

The long form occurs naturally, as the start and stop codons wereidentified from human brain cDNA that was reverse-transcribed fromnatural transcripts. The short form may result from the long form by amodifying mechanism, e.g., from an alternative splicing of thetranscript or from an independent transcript generated at a separategenomic locus, but whether that is true or not is irrelevant to thisinvention.

As used herein, the phrase an isolated or recombinant receptorcomprising an amino acid sequence “defined by SEQ ID NO: 4, or asubsequence thereof” is thus defined to include both “short” and “long”forms of the human GalR3 receptor.

The present invention also encompasses fragments, analogs and physicalvariants of the receptors. As used herein, the term “polypeptide” or“peptide” means a fragment or segment, e.g., of a mammalian galaninreceptor having an amino acid sequence defined by SEQ ID NO: 2 or 4which comprises a subsequence of the complete amino acid sequence of thereceptor containing at least about 8, preferably at least about 12, morepreferably at least about 20, and most preferably at least about 30 ormore contiguous amino acid residues, up to and including the totalnumber of residues in the complete receptor.

The polypeptides of the invention can comprise any part of the completesequence of such a receptor. Thus, although they could be produced byproteolytic cleavage of an intact receptor, they can also be made bychemical synthesis or by the application of recombinant DNA technologyand are not limited to polypeptides delineated by proteolytic cleavagesites. The polypeptides, either alone or cross-linked or conjugated to acarrier molecule to render them more immunogenic, are useful as antigensto elicit the production of antibodies. The antibodies can be used,e.g., in immunoassays of the intact receptors, for immunoaffinitypurification, etc.

The term “analog(s)” means a mammalian galanin receptor of the inventionwhich has been modified by deletion, addition, modification orsubstitution of one or more amino acid residues in the wild-typereceptor. It encompasses allelic and polymorphic variants, and alsomuteins and fusion proteins which comprise all or a significant part ofsuch a mammalian galanin receptor, e.g., covalently linked via aside-chain group or terminal residue to a different protein, polypeptideor moiety (fusion partner).

Some amino acid substitutions are preferably “conservative”, withresidues replaced with physicochemically similar residues, such asGly/Ala, Asp/Glu, Val/Ile/Leu, Lys/Arg, Asn/Gln and Phe/Trp/Tyr. Analogshaving such conservative substitutions typically retain substantialgalanin binding activity. Other analogs, which have non-conservativesubstitutions such as Asn/Glu, Val/Tyr and His/Glu, may substantiallylack such activity. Nevertheless, such analogs are useful because theycan be used as antigens to elicit production of antibodies in animmunologically competent host. Because these analogs retain many of theepitopes (antigenic determinants) of the wild-type receptors from whichthey are derived, many antibodies produced against them can also bind tothe active-conformation or denatured wild-type receptors. Accordingly,such antibodies can also be used, e.g., for the immunopurification orimmunoassay of the wild-type receptors.

Some analogs are truncated variants in which residues have beensuccessively deleted from the amino- and/or carboxyl-termini, whilesubstantially retaining the characteristic ligand binding activity.

Modifications of amino acid residues may include but are not limited toaliphatic esters or amides of the carboxyl terminus or of residuescontaining carboxyl side chains. O-acyl derivatives of hydroxylgroup-containing residues, and N-acyl derivatives of the amino-terminalamino acid or amino-group containing residues, e.g., lysine or arginine.

Other analogs are mammalian galanin receptors containing modifications,such as incorporation of unnatural amino acid residues, orphosphorylated amino acid residues such as phosphotyrosine,phosphoserine or phosphothreonine residues. Other potentialmodifications include sulfonation, biotinylation, or the addition ofother moieties, particularly those which have molecular shapes similarto phosphate groups.

Analogs of the mammalian galanin receptors can be prepared by chemicalsynthesis or by using site-directed mutagenesis [Gillman et al., Gene8:81 (1979); Roberts et al., Nature 328:731 (1987) or Innis (Ed.), 1990,PCR Protocols: A Guide to Methods and Applications, Academic Press, NewYork, N.Y.] or the polymerase chain reaction method [PCR; Saiki et al.,Science 239:487 (1988)], as exemplified by Daugherty et al. [NucleicAcids Res. 19:2471 (1991)] to modify nucleic acids encoding the completereceptors. Adding epitope tags for purification or detection ofrecombinant products is envisioned.

General techniques for nucleic acid manipulation and expression that canbe used to make the analogs are described generally, e.g., in Sambrook,et al., Molecular Cloning: A Laboratory Manual (2d ed.), 1989, Vols.1-3, Cold Spring Harbor Laboratory. Techniques for the synthesis ofpolypeptides are described, for example, in Merrifield, J. Amer. Chem.Soc. 85:2149 (1963); Merrifield, Science 232:341 (1986); and Atherton etal., Solid Phase Peptide Synthesis: A Practical Approach, 1989, IRLPress, Oxford.

Still other analogs are prepared by the use of agents known in the artfor their usefulness in cross-linking proteins through reactive sidegroups. Preferred derivatization sites with cross-linking agents arefree amino groups, carbohydrate moieties and cysteine residues.

Substantial retention of ligand binding activity by the foregoinganalogs of the mammalian galanin receptors typically entails retentionof at least about 50%, preferably at least about 75%, more preferably atleast about 80%, and most preferably at least about 90% of the galaninbinding activity and/or specificity of the corresponding wild-typereceptor.

Some of the physical variants have substantial amino acid sequencehomology with the amino acid sequences of the mammalian galaninreceptors or polypeptides. In this invention, amino acid sequencehomology, or sequence identity, is determined by optimizing residuematches and, if necessary, by introducing gaps as required. Homologousamino acid sequences are typically intended to include natural allelic,polymorphic and interspecies variations in each respective sequence.

Typical homologous proteins or peptides will have from 25-100% homology(if gaps can be introduced) to 50-100% homology (if conservativesubstitutions are included), with the amino acid sequence of the galaninreceptors. Primate species receptors are of particular interest.

Observed homologies will typically be at least about 35%, preferably atleast about 50%, more preferably at least about 75%, and most preferablyat least about 80% or more. See Needleham et al., J. Mol. Biol.48:443-453 (1970); Sankoff et al. in Time Warps, String Edits, andMacromolecules: The Theory and Practice of Sequence Comparison, 1983,Addison-Wesley, Reading, Mass.; and software packages fromIntelliGenetics, Mountain View, Calif., and the University of WisconsinGenetics Computer Group, Madison, Wis.

Glycosylation variants include, e.g., analogs made by modifyingglycosylation patterns during synthesis and processing in variousalternative eukaryotic host expression systems, or during furtherprocessing steps. Particularly preferred methods for producingglycosylation modifications include exposing the mammalian galaninreceptors to glycosylating enzymes derived from cells which normallycarry out such processing, such as mammalian glycosylation enzymes.Alternatively, deglycosylation enzymes can be used to removecarbohydrates attached during production in eukaryotic expressionsystems.

Protein Purification

The proteins, polypeptides and antigenic fragments of this invention canbe purified by standard methods, including but not limited to salt oralcohol precipitation, preparative disc-gel electrophoresis, isoelectricfocusing, high pressure liquid chromatography (HPLC), reversed-phaseHPLC, gel filtration, cation and anion exchange and partitionchromatography, and countercurrent distribution. Such purificationmethods are well known in the art and are disclosed, e.g., in Guide toProtein Purification, Methods in Enzymology, Vol. 182, M. Deutscher,Ed., 1990, Academic Press, New York, N.Y. More specific methodsapplicable to purification of the galanin receptors are described below.

Purification steps can be followed by carrying out assays for ligandbinding activity as described below. Particularly where a receptor isbeing isolated from a cellular or tissue source, it is preferable toinclude one or more inhibitors of proteolytic enzymes is the assaysystem, such as phenylmethanesulfonyl fluoride (PMSF).

Antibody Production

Antigenic (i.e., immunogenic) fragments of the mammalian galaninreceptors of this invention, which may or may not have ligand bindingactivity, may similarly be produced. Regardless of whether they bindgalanin, such fragments, like the complete receptors, are useful asantigens for preparing antibodies by standard methods that can bind tothe complete receptors. Shorter fragments can be concatenated orattached to a carrier. Because it is well known in the art that epitopesgenerally contain at least about five, preferably at least about 8,amino acid residues [Ohno et al., Proc. Natl. Acad. Sci. USA 82:2945(1985)], fragments used for the production of antibodies will generallybe at least that size. Preferably, they will contain even more residues,as described above. Whether a given fragment is immunogenic can readilybe determined by routine experimentation.

Although it is generally not necessary when complete mammalian galaninreceptors are used as antigens to elicit antibody production in animmunologically competent host, smaller antigenic fragments arepreferably first rendered more immunogenic by cross-linking orconcatenation, or by coupling to an immunogenic carrier molecule (i.e.,a macromolecule having the property of independently eliciting animmunological response in a host animal). Cross-linking or conjugationto a carrier molecule may be required because small polypeptidefragments sometimes act as haptens (molecules which are capable ofspecifically binding to an antibody but incapable of eliciting antibodyproduction, i.e., they are not immunogenic). Conjugation of suchfragments to an immunogenic carrier molecule renders them moreimmunogenic through what is commonly known as the “carrier effect”.

Suitable carrier molecules include, e.g., proteins and natural orsynthetic polymeric compounds such as polypeptides, polysaccharides,lipopolysaccharides etc. Protein carrier molecules are especiallypreferred, including but not limited to keyhole limpet hemocyanin andmammalian serum proteins such as human or bovine gammaglobulin, human,bovine or rabbit serum albumin, or methylated or other derivatives ofsuch proteins. Other protein carriers will be apparent to those skilledin the art. Preferably, but not necessarily, the protein carrier will beforeign to the host animal in which antibodies against the fragments areto be elicited.

Covalent coupling to the carrier molecule can be achieved using methodswell known in the art, the exact choice of which will be dictated by thenature of the carrier molecule used. When the immunogenic carriermolecule is a protein, the fragments of the invention can be coupled,e.g., using water soluble carbodiimides such as dicyclohexylcarbodiimideor glutaraldehyde.

Coupling agents such as these can also be used to cross-link thefragments to themselves without the use of a separate carrier molecule.Such cross-linking into aggregates can also increase immunogenicity.Immunogenicity can also be increased by the use of known adjuvants,alone or in combination with coupling or aggregation.

Suitable adjuvants for the vaccination of animals include but are notlimited to Adjuvant 65 (containing peanut oil, mannide monooleate andaluminum monostearate); Freund's complete or incomplete adjuvant;mineral gels such as aluminum hydroxide, aluminum phosphate and alum;surfactants such as hexadecylamine, octadecylamine, lysolecithin,dimethyldioctadecylammonium bromide,N,N-dioctadecyl-N′,N′-bis(2-hydroxymethyl) propanediamine,methoxyhexadecylglycerol and pluronic polyols; polyanions such as pyran,dextran sulfate, poly IC, polyacrylic acid and carbopol; peptides suchas muramyl dipeptide, dimethylglycine and tuftsin; and oil emulsions.The polypeptides could also be administered following incorporation intoliposomes or other microcarriers.

Information concerning adjuvants and various aspects of immunoassays aredisclosed, e.g., in the series by P. Tijssen, Practice and Theory ofEnzyme Immunoassays, 3rd Edition, 1987, Elsevier, New York. Other usefulreferences covering methods for preparing polyclonal antisera includeMicrobiology, 1969, Hoeber Medical Division, Harper and Row;Landsteiner, Specificity of Serological Reactions, 1962, DoverPublications, New York, and Williams, et al., Methods in Immunology andImmunochemistry, Vol. 1, 1967, Academic Press, New York.

Serum produced from animals immunized using standard methods can be useddirectly, or the IgG fraction can be separated from the serum usingstandard methods such as plasmaphoresis or adsorption chromatographywith IgG-specific adsorbents such as immobilized Protein A.Alternatively, monoclonal antibodies can be prepared.

Hybridomas producing monoclonal antibodies against the galanin receptorsof the invention or antigenic fragments thereof are produced bywell-known techniques. Usually, the process involves the fusion of animmortalizing cell line with a B-lymphocyte that produces the desiredantibody. Alternatively, non-fusion techniques for generating immortalantibody-producing cell lines can be used, e.g., virally-inducedtransformation [Casali et al., Science 234:476 (1986)]. Immortalizingcell lines are usually transformed mammalian cells, particularly myelomacells of rodent, bovine, and human origin. Most frequently, rat or mousemyeloma cell lines are employed as a matter of convenience andavailability.

Techniques for obtaining antibody-producing lymphocytes from mammalsinjected with antigens are well known. Generally, peripheral bloodlymphocytes (PBLs) are used if cells of human origin are employed, orspleen or lymph node cells are used from non-human mammalian sources. Ahost animal is injected with repeated dosages of the purified antigen(human cells are sensitized in vitro), and the animal is permitted togenerate the desired antibody-producing cells before they are harvestedfor fusion with the immortalizing cell line. Techniques for fusion arealso well known in the art, and in general involve mixing the cells witha fusing agent, such as polyethylene glycol.

Hybridomas are selected by standard procedures, such as HAT(hypoxanthine-aminopterin-thymidine) selection. Those secreting thedesired antibody are selected using standard immunoassays, such asWestern blotting, ELISA (enzyme-linked immunosorbent assay), RIA(radioimmunoassay), or the like. Antibodies are recovered from themedium using standard protein purification techniques [Tijssen, Practiceand Theory of Enzyme Immunoassays (Elsevier, Amsterdam, 1985)].

Many references are available to provide guidance in applying the abovetechniques [Kohler et al., Hybridoma Techniques (Cold Spring HarborLaboratory, New York, 1980); Tijssen, Practice and Theory of EnzymeImmunoassays (Elsevier, Amsterdam, 1985); Campbell, Monoclonal AntibodyTechnology (Elsevier, Amsterdam, 1984); Hurrell, Monoclonal HybridomaAntibodies: Techniques and Applications (CRC Press, Boca Raton, Fla.,1982)]. Monoclonal antibodies can also be produced using well knownphage library systems. See, e.g., Huse, et al., Science 246:1275 (1989);Ward, et al., Nature 341:544 (1989).

Antibodies thus produced, whether polyclonal or monoclonal, can be used,e.g., in an immobilized form bound to a solid support by well knownmethods, to purify the receptors by immunoaffinity chromatography.

Antibodies against the antigenic fragments can also be used, unlabeledor labeled by standard methods, as the basis for immunoassays of themammalian galanin receptors. The particular label used will depend uponthe type of immunoassay. Examples of labels that can be used include butare not limited to radiolabels such as ³²P, ¹²⁵I, ³H and ¹⁴C;fluorescent labels such as fluorescein and its derivatives, rhodamineand its derivatives, dansyl and umbelliferone; chemilluminescers such asluciferase and 2,3-dihydrophthalazinediones; and enzymes such ashorseradish peroxidase, alkaline phosphatase, lysozyme andglucose-6-phosphate dehydrogenase.

The antibodies can be tagged with such labels by known methods. Forexample, coupling agents such as aldehydes, carbodiimides, dimaleimide,imidates, succinimides, bisdiazotized benzadine and the like may be usedto tag the antibodies with fluorescent, chemilluminescent or enzymelabels. The general methods involved are well known in the art and aredescribed, e.g., in Immunoassay: A Practical Guide, 1987, Chan (Ed.),Academic Press, Inc., Orlando, Fla. Such immunoassays could be carriedout, for example, on fractions obtained during purification of thereceptors.

The antibodies of the present invention can also be used to identifyparticular cDNA clones expressing the galanin receptors in expressioncloning systems.

Neutralizing antibodies specific for the ligand binding site of areceptor can also be used as antagonists (inhibitors) to block galaninbinding. Such neutralizing antibodies can readily be identified throughroutine experimentation, e.g., by using the radioligand binding assaydescribed infra. Antagonism of galanin activity can be accomplishedusing complete antibody molecules, or well known antigen bindingfragments such as Fab, Fc, F(ab)₂, and Fv fragments.

Definitions of such fragments can be found, e.g., in Klein, Immunology(John Wiley, New York, 1982); Parham, Chapter 14, in Weir, ed.Immunochemistry, 4th Ed. (Blackwell Scientific Publishers, Oxford,1986). The use and generation of antibody fragments has also beendescribed, e.g.: Fab fragments [Tijssen, Practice and Theory of EnzymeImmunoassays (Elsevier, Amsterdam, 1985)], Fv fragments [Hochman et al.,Biochemistry 12:1130 (1973); Sharon et al., Biochemistry 15:1591 (1976);Ehrlich et al., U.S. Pat. No. 4,355,023] and antibody half molecules(Auditore-Hargreaves, U.S. Pat. No. 4,470,925). Methods for makingrecombinant Fv fragments based on known antibody heavy and light chainvariable region sequences have further been described, e.g., by Moore etal. (U.S. Pat. No. 4,642,334) and by Plückthun [Bio/Technology 9:545(1991)]. Alternatively, they can be chemically synthesized by standardmethods.

Anti-idiotypic antibodies, both polyclonal and monoclonal, can also beproduced using the antibodies elicited against the receptors asantigens. Such antibodies can be useful as they may mimic the receptors.

Nucleic Acids and Expression Vectors

As used herein, the term “isolated nucleic acid” means a nucleic acidsuch as an RNA or DNA molecule, or a mixed polymer, which issubstantially separated from other components that are normally found incells or in recombinant DNA expression systems. These components includebut are not limited to ribosomes, polymerases, serum components, andflanking genomic sequences. The term thus embraces a nucleic acid whichhas been removed from its naturally occurring environment, and includesrecombinant or cloned DNA isolates and chemically synthesized analogs oranalogs biologically synthesized by heterologous systems. Asubstantially pure molecule includes isolated forms of the molecule.

An isolated nucleic acid will generally be a homogeneous composition ofmolecules but may, in some embodiments, contain minor heterogeneity.Such heterogeneity is typically found at the ends of nucleic acid codingsequences or in regions not critical to a desired biological function oractivity.

A “recombinant nucleic acid” is defined either by its method ofproduction or structure. Some recombinant nucleic acids are thus made bythe use of recombinant DNA techniques which involve human intervention,either in manipulation or selection. Others are made by fusing twofragments not naturally contiguous to each other. Engineered vectors areencompassed, as well as nucleic acids comprising sequences derived usingany synthetic oligonucleotide process.

For example, a wild-type codon may be replaced with a redundant codonencoding the same amino acid residue or a conservative substitution,while at the same time introducing or removing a nucleic acid sequencerecognition site. Similarly, nucleic acid segments encoding desiredfunctions may be fused to generate a single genetic entity encoding adesired combination of functions not found together in nature. Althoughrestriction enzyme recognition sites are often the target of suchartificial manipulations, other site-specific targets, e.g., promoters,DNA replication sites, regulation sequences, control sequences, or otheruseful features may be incorporated by design. Sequences encodingepitope tags for detection or purification as described above may alsobe incorporated.

A nucleic acid “fragment” is defined herein as a nucleotide sequencecomprising at least about 17, generally at least about 25, preferably atleast about 35, more preferably at least about 45, and most preferablyat least about 55 or more contiguous nucleotides.

This invention further encompasses recombinant DNA molecules andfragments having sequences that are identical or highly homologous tothose described herein. The nucleic acids of the invention may beoperably linked to DNA segments which control transcription,translation, and DNA replication.

“Homologous nucleic acid sequences” are those which when aligned andcompared exhibit significant similarities. Standards for homology innucleic acids are either measures for homology generally used in the artby sequence comparison or based upon hybridization conditions, which aredescribed in greater detail below.

Substantial nucleotide sequence homology is observed when there isidentity in nucleotide residues in two sequences (or in theircomplementary strands) when optimally aligned to account for nucleotideinsertions or deletions, in at least about 50%, preferably in at leastabout 75%, more preferably in at least about 90%, and most preferably inat least about 95% of the aligned nucleotides.

Substantial homology also exists when one sequence will hybridize underselective hybridization conditions to another. Typically, selectivehybridization will occur when there is at least about 55% homology overa stretch of at least about 30 nucleotides, preferably at least about65% over a stretch of at least about 25 nucleotides, more preferably atleast about 75%, and most preferably at least about 90% over about 20nucleotides. See, e.g., Kanehisa, Nucleic Acids Res. 12:203 (1984).

The lengths of such homology comparisons may encompass longer stretchesand in certain embodiments may cover a sequence of at least about 17,preferably at least about 25, more preferably at least about 50, andmost preferably at least about 75 nucleotide residues.

Stringency of conditions employed in hybridizations to establishhomology are dependent upon factors such as salt concentration,temperature, the presence of organic solvents, and other parameters.Stringent temperature conditions usually include temperatures in excessof about 30° C., often in excess of about 37° C., typically in excess ofabout 45° C., preferably in excess of about 55° C., more preferably inexcess of about 65° C., and most preferably in excess of about 70° C.Stringent salt conditions will ordinarily be less than about 1000 mM,usually less than about 500 mM, more usually less than about 400 mM,preferably less than about 300 mM, more preferably less than about 200mM, and most preferably less than about 150 mM. For example, saltconcentrations of 100, 50 and 20 mM are used. The combination of theforegoing parameters, however, is more important than the measure of anysingle parameter. See, e.g., Wetmur et al., J. Mol. Biol. 31:349 (1968).

The term “substantially pure” is defined herein to mean a mammaliangalanin receptor, nucleic acid or other material that is free from othercontaminating proteins, nucleic acids, and other biologicals derivedfrom an original source organism or recombinant DNA expression system.Purity may be assayed by standard methods and will typically exceed atleast about 50%, preferably at least about 75%, more preferably at leastabout 90%, and most preferably at least about 95% purity. Purityevaluation may be made on a mass or molar basis.

Nucleic acids encoding the galanin receptors or fragments thereof can beprepared by standard methods. For example, DNA can be chemicallysynthesized using, e.g., the phosphoramidite solid support method ofMatteucci et al. [J. Am. Chem. Soc. 103:3185 (1981)], the method of Yooet al. [J. Biol. Chem. 764:17078 (1989)], or other well known methods.This can be done by sequentially linking a series of oligonucleotidecassettes comprising pairs of synthetic oligonucleotides, as describedbelow.

Of course, due to the degeneracy of the genetic code, many differentnucleotide sequences can encode the galanin receptors. The codons can beselected for optimal expression in prokaryotic or eukaryotic systems.Such degenerate variants are of course also encompassed by thisinvention.

Moreover, nucleic acids encoding the galanin receptors can readily bemodified by nucleotide substitutions, nucleotide deletions, nucleotideinsertions, and inversions of nucleotide stretches. Such modificationsresult in novel DNA sequences which encode antigens having immunogenicor antigenic activity in common with the wild-type receptors. Thesemodified sequences can be used to produce wild-type or mutant receptors,or to enhance expression in a recombinant DNA system.

Insertion of the DNAs encoding the galanin receptors into a vector iseasily accomplished when the termini of both the DNAs and the vectorcomprise compatible restriction sites. If this cannot be done, it may benecessary to modify the termini of the DNAs and/or vector by digestingback single-stranded DNA overhangs generated by restriction endonucleasecleavage to produce blunt ends, or to achieve the same result by fillingin the single-stranded termini with an appropriate DNA polymerase.

Alternatively, desired sites may be produced, e.g., by ligatingnucleotide sequences (linkers) onto the termini. Such linkers maycomprise specific oligonucleotide sequences that define desiredrestriction sites. Restriction sites can also be generated by the use ofthe polymerase chain reaction (PCR). See, e.g., Saiki et al., Science239:487 (1988). The cleaved vector and the DNA fragments may also bemodified if required by homopolymeric tailing.

Recombinant expression vectors used in this invention are typicallyself-replicating DNA or RNA constructs comprising nucleic acids encodingone of the mammalian GalR3 receptors, usually operably linked tosuitable genetic control elements that are capable of regulatingexpression of the nucleic acids in compatible host cells. Geneticcontrol elements may include a prokaryotic promoter system or aeukaryotic promoter expression control system, and typically include atranscriptional promoter, an optional operator to control the onset oftranscription, transcription enhancers to elevate the level of mRNAexpression, a sequence that encodes a suitable ribosome binding site,and sequences that terminate transcription and translation. Expressionvectors also may contain an origin of replication that allows the vectorto replicate independently of the host cell.

Vectors that could be used in this invention include microbial plasmids,viruses, bacteriophage, integratable DNA fragments, and other vehicleswhich may facilitate integration of the nucleic acids into the genome ofthe host. Plasmids are the most commonly used form of vector but allother forms of vectors which serve an equivalent function and which are,or become, known in the art are suitable for use herein. See, e.g.,Pouwels et al., Cloning Vectors: A Laboratory Manual, 1985 andSupplements, Elsevier, N.Y., and Rodriguez et al. (eds.), Vectors: ASurvey of Molecular Cloning Vectors and Their Uses, 1988, Buttersworth,Boston, Mass.

Expression of nucleic acids encoding the galanin receptors of thisinvention can be carried out by conventional methods in eitherprokaryotic or eukaryotic cells. Although strains of E. coli areemployed most frequently in prokaryotic systems, many other bacteriasuch as various strains of Pseudomonas and Bacillus are know in the artand can be used as well.

Prokaryotic expression control sequences typically used includepromoters, including those derived from the β-lactamase and lactosepromoter systems [Chang et al., Nature 198:1056 (1977)], the tryptophan(trp) promoter system [Goeddel et al., Nucleic Acids Res. 8:4057(1980)], the lambda P_(L) promoter system [Shimatake et al., Nature292:128 (1981)] and the tac promoter [De Boer et al., Proc. Natl. Acad.Sci. USA 292:128 (1983)]. Numerous expression vectors containing suchcontrol sequences are known in the art and available commercially.

Suitable host cells for expressing nucleic acids encoding the mammalianGalR3 receptors include prokaryotes and higher eukaryotes. Prokaryotesinclude both gram negative and positive organisms, e.g., E. coli and B.sutbtilis. Higher eukaryotes include established tissue culture celllines from animal cells, both of non-mammalian origin, e.g., insectcells, and birds, and of mammalian origin, e.g., human, primates, androdents.

Prokaryotic host-vector systems include a wide variety of vectors formany different species. As used herein, E. coli and its vectors will beused generically to include equivalent vectors used in otherprokaryotes. A representative vector for amplifying DNA is pBR322 ormany of its derivatives. Vectors that can be used to express themammalian GalR3 receptors include but are not limited to thosecontaining the lac promoter (pUC-series); trp promoter (pBR322-trp); Ipppromoter (the pIN-series); lambda-pP or pR promoters (pOTS); or hybridpromoters such as ptac (pDR540). See Brosius et al., “Expression VectorsEmploying Lambda-, trp-, lac-, and Ipp-derived Promoters”, in Rodriguezand Denhardt (eds.) Vectors: A Survey of Molecular Cloning Vectors andTheir Uses, 1988, Buttersworth, Boston, pp. 205-236.

Higher eukaryotic tissue culture cells are preferred hosts for therecombinant production of the mammalian GalR3 receptors. Although anyhigher eukaryotic tissue culture cell line might be used, includinginsect baculovirus expression systems, mammalian cells are preferred.Transformation or transfection and propagation of such cells has becomea routine procedure. Examples of useful cell lines include HeLa cells,Chinese hamster ovary (CHO) cell lines, baby rat kidney (BRK) celllines, insect cell lines, bird cell lines, and monkey (COS) cell lines.

Expression vectors for such cell lines usually include an origin ofreplication, a promoter, a translation initiation site, RNA splice sites(if genomic DNA is used), a polyadenylation site, and a transcriptiontermination site. These vectors also usually contain a selection gene oramplification gene. Suitable expression vectors may be plasmids,viruses, or retroviruses carrying promoters derived, e.g., from suchsources as adenovirus, SV40, parvoviruses, vaccinia virus, orcytomegalovirus. Representative examples of suitable expression vectorsinclude pCR®3.1, pcDNA1, pCD [Okayama et al., Mol. Cell. Biol. 5:1136(1985)], pMC1neo Poly-A [Thomas et al., Cell 51:503 (1987)], pUC19,pREP8, pSVSPORT and derivatives thereof, and baculovirus vectors such aspAC 373 or pAC 610.

Pharmaceutical Compositions

The antibodies and antigen-binding fragments thereof can be usedtherapeutically to block the activity of galanin, and thereby to treatany medical condition caused or mediated by galanin. Such antibodies andfragments are preferably chimeric or humanized, to reduce antigenicityand human anti-mouse antibody (HAMA) reactions. The methodology involvedis disclosed, e.g., in U.S. Pat. No. 4,816,397 to Boss et al. and inU.S. Pat. No. 4,816,567 to Cabilly et al. Further refinements onantibody humanization are described in European Patent 451 216 B1.

The dosage regimen involved in a therapeutic application will bedetermined by the attending physician, considering various factors whichmay modify the action of the antibodies or binding fragments, e.g., thecondition, body weight, sex and diet of the patient, the severity of anyinfection, time of administration, and other clinical factors.

Typical protocols for the therapeutic administration of antibodies arewell known in the art and have been disclosed, e.g., by Elliott et al.[The Lancet 344:1125 (1994)], Isaacs et al. [The Lancet 340:748 (1992)],Anasetti et al. [Transplantation 54:844 (1992)], Anasetti et al. [Blood84:1320 (1994)], Hale et al. [The Lancet 2:1394 (Dec. 17, 1988)], Queen[Scrip 1881:18 (1993)] and Mathieson et al. [N. Eng. J. Med. 323:250(1990)].

Administration of the compositions of this invention is typicallyparenteral, by intraperitoneal, intravenous, subcutaneous, orintramuscular injection, or by infusion or by any other acceptablesystemic method. Administration by intravenous infusion, typically overa time course of about 1 to 5 hours, is preferred.

Often, treatment dosages are titrated upward from a low level tooptimize safety and efficacy. Generally, daily antibody dosages willfall within a range of about 0.01 to 20 mg protein per kilogram of bodyweight. Typically, the dosage range will be from about 0.1 to 5 mgprotein per kilogram of body weight.

Dosages of antigen binding fragments from the antibodies will beadjusted to account for the smaller molecular sizes and possiblydecreased half-lives (clearance times) following administration. Variousmodifications or derivatives of the antibodies or fragments, such asaddition of polyethylene glycol chains (PEGylation), may be made toinfluence their pharmacokinetic and/or pharmacodynamic properties.

It will be appreciated by those skilled in the art, however, that thegalanin antagonists of the invention are not limited to neutralizingantibodies or binding fragments thereof. This invention also encompassesother types of inhibitors, including small organic molecules andinhibitory ligand analogs, which can be identified using the methods ofthe invention.

An “effective amount” of a composition of the invention is an amountthat will ameliorate one or more of the well known parameters thatcharacterize medical conditions caused or mediated by galanin. Many suchparameters and conditions have been described, e.g., as in reviews byBantfa (Psychopharmacology: The Fourth Generation of Progress, 1995, F.E. Bloom and D. J. Kupfer, Eds., Ravin Press, Ltd., New York, N.Y., pp.563-571) and Crawley [Life Science 58:2185-2199 (1996)].

Although the compositions of this invention could be administered insimple solution, they are more typically used in combination with othermaterials such as carriers, preferably pharmaceutical carriers. Usefulpharmaceutical carriers can be any compatible, non-toxic substancesuitable for delivering the compositions of the invention to a patient.Sterile water, alcohol, fats, waxes, and inert solids may be included ina carrier. Pharmaceutically acceptable adjuvants (buffering agents,dispersing agents) may also be incorporated into the pharmaceuticalcomposition. Generally, compositions useful for parenteraladministration of such drugs are well known; e.g. Remington'sPharmaceutical Science, 17th Ed. (Mack Publishing Company, Easton, Pa.,1990). Alternatively, compositions of the invention may be introducedinto a patient's body by implantable drug delivery systems [Urquhart etal., Ann. Rev. Pharmacol. Toxicol. 24:199 (1984)].

Therapeutic formulations may be administered in many conventional dosageformulation. Formulations typically comprise at least one activeingredient, together with one or more pharmaceutically acceptablecarriers. Formulations may include those suitable for oral, rectal,nasal, or parenteral (including subcutaneous, intramuscular, intravenousand intradermal) administration.

The formulations may conveniently be presented in unit dosage form andmay be prepared by any methods well known in the art of pharmacy. See,e.g., Gilman et al. (eds.) (1990), The Pharmacological Bases ofTherapeutics, 8th Ed., Pergamon Press; and Remington's PharmaceuticalSciences, supra, Easton, Pa.; Avis et al. (eds.) (1993) PharmaceuticalDosage Forms: Parenteral Medications Dekker, New York; Lieberman et al.(eds.) (1990) Pharmaceutical Dosage Forms: Tablets Dekker, New York; andLieberman et al. (eds.) (1990), Pharmaceutical Dosage Forms: DisperseSystems Dekker, New York.

The present invention also encompasses anti-idiotypic antibodies, bothpolyclonal and monoclonal, which are produced using the above-describedantibodies as antigens. These antibodies are useful because they maymimic the structures of the receptors.

Screening Systems and Methods

The galanin receptors of this invention can be employed in screeningsystems to identify agonists or antagonists of the receptors.Essentially, these systems provide methods for bringing together amammalian galanin receptor, an appropriate known ligand, includinggalanin itself, and a sample to be tested for the presence of a galaninagonist or antagonist.

Two basic types of screening systems can be used, a labeled-ligandbinding assay and a “functional” assay. A labeled ligand for use in thebinding assay can be obtained by labeling galanin or a known galaninagonist with a measurable group as described above in connection withthe labeling of antibodies. Various labeled forms of galanin areavailable commercially. In an example below, ¹²⁵I-galanin is used as theligand.

Typically, a given amount of one of the galanin receptors of theinvention is contacted with increasing amounts of a labeled ligand, suchas labeled galanin itself, and the amount of the bound labeled ligand ismeasured after removing unbound labeled ligand by washing. As the amountof the labeled ligand is increased, a point is eventually reached atwhich all receptor binding sites are occupied or saturated. A plot ofsuch binding is shown in FIG. 1. Specific receptor binding of thelabeled ligand is abolished by a large excess of unlabeled ligand.

Preferably, an assay system is used in which non-specific binding of thelabeled ligand to the receptor is minimal. Non-specific binding istypically less than 50%, preferably less than 15%, and more preferablyless than 10% of the total binding of the labeled ligand.

As used herein, the term “galanin ligand” is defined to mean galaninitself or a fragment thereof comprising at least about the fifteenamino-terminal residues of galanin, and extending up to the completegalanin molecule. The amino acid sequence of the amino-terminal residuesis conserved in the galanins of various species, including humans.Therefore, galanin from one species may bind to galanin receptors fromanother species; e.g., porcine galanin binds to the rat receptor, as isillustrated in an Example below. For regulatory purposes, however, itmay be desirable to use human galanin or an active fragment thereof asthe galanin ligand in conjunction with the human receptor when screeningfor galanin agonists or antagonists for human therapeutic purposes.

In principle, a binding assay of the invention could be carried outusing a soluble receptor of the invention, e.g., following productionand refolding by standard methods from an E. coli expression system, andthe resulting receptor-labeled ligand complex could be precipitated,e.g., using an antibody against the receptor. The precipitate could thenbe washed and the amount of the bound labeled ligand could be measured.

Preferably, however, a nucleic acid encoding one of the galaninreceptors of the invention is transfected into an appropriate host cell,whereby the receptor will become incorporated into the membrane of thecell. A membrane fraction can then be isolated from the cell and used asa source of the receptor for assay. Preferably, specific binding of thelabeled ligand to a membrane fraction from the untransfected host cellwill be negligible, as is the case with COS-7 cells used in an Examplebelow.

The binding assays of this invention can be used to identify bothgalanin agonists and antagonists, because both will compete for bindingto the receptor with the labeled ligand.

In the basic binding assay, the method for identifying a galanin agonistor antagonist comprises:

-   -   (a) contacting a mammalian GalR3 receptor having an amino acid        sequence defined by SEQ ID NO: 2 or SEQ ID NO: 4, or a        subsequence thereof, in the presence of a known amount of        labeled galanin with a sample to be tested for the presence of a        galanin agonist or antagonist; and    -   (b) measuring the amount of labeled galanin bound to the        receptor;        whereby a galanin agonist or antagonist in the sample is        identified by measuring substantially reduced binding of the        labeled galanin to the GalR3 receptor, compared to what would be        measured in the absence of such agonist or antagonist.

Preferably, the GalR3 receptor used to identify a galanin agonist orantagonist for human therapeutic purposes has an amino acid sequencedefined by SEQ ID NO: 4, or a subsequence thereof.

In one embodiment of the invention, the foregoing method furthercomprises:

-   -   (c) contacting a mammalian GalR1 or GalR2 receptor in the        presence of a known amount of labeled galanin with a compound        identified as a galanin agonist or antagonist in steps (a) and        (b); and

(d) measuring the amount of labeled galanin bound to the receptor;whereby a galanin agonist or antagonist specific for the GalR3 receptoris identified by measuring substantially undiminished binding of thelabeled galanin to the receptor, compared to what would be measured inthe absence of such agonist or antagonist.

Determination of whether a particular molecule inhibiting binding of thelabeled ligand to the receptor is an antagonist or an agonist is thendetermined in a second, functional assay. The functionality of GalR3agonists and antagonists identified in the binding assay can bedetermined in cellular and animal models.

In cellular models, parameters for intracellular activities mediated bygalanin receptors can be monitored for antagonistic and/or agonisticactivities. Such parameters include but are not limited to intracellularsecond messenger pathways activated via the GalR3 receptors, changes incell growth rate, secretion of hormones, etc., using published methods.Examples of the methods are measurement of the effects of the ligands onreceptor-mediated inhibition of forskolin-stimulated intracellular cAMPproduction [Parker et al., Mol. Brain. Res. 34:179-189 (1995)],receptor-stimulated Ca⁺⁺ mobilization and mitogenic effects [Sethi etal., Cancer Res. 51:1674-1679 (1991)], and receptor-mediatedglucose-stimulated insulin release [Yanaihara et al., RegulatoryPeptides 46:93-101 (1993)].

In animal models, physiological effects of the agonists and antagonistscan be evaluated by feeding the compounds and observing changes infeeding behavior and body weight [Crawley et al., Brain Res. 600:268-272(1993)], acetylcholine release [Ogren et al., Eur. J. Pharmacology242:59-64 (1993)], learning [Ogren et al., Neuroscience 51:1-5 (1992)],memory [Robinsin et al., Behav. Neurosci. 107:458-467 (1993)], and painmodulation [Verge et al., Neuroscience Letters 149:193-197 (1993)].

Other Mammalian GalR3Receptors

The present invention provides methods for cloning mammalian GalR3receptors from other mammalian species. Briefly, Southern and Northernblot analysis can be carried out to identify cells from other speciesexpressing genes encoding the GalR3 receptors. Complementary DNA (cDNA)libraries can be prepared by standard methods from mRNA isolated fromsuch cells, and degenerate probes or PCR primers based on the nucleicacid and amino acid sequences provided herein can be used to identifyclones encoding a GalR3 receptor.

Alternatively, expression cloning methodology can be used to identifyparticular clones encoding a GalR3 receptor. An antibody preparationwhich exhibits cross-reactivity with GalR3 receptors from a number ofmammalian species may be useful in monitoring expression cloning.

However identified, clones encoding GalR3 receptors from variousmammalian species can be isolated and sequenced, and the coding regionscan be excised and inserted into an appropriate vector.

EXAMPLES

The present invention can be illustrated by the following examples.Unless otherwise indicated, percentages given below for solids in solidmixtures, liquids in liquids, and solids in liquids are on a wt/wt,vol/vol and wt/vol basis, respectively. Sterile conditions weregenerally maintained during cell culture.

Materials and General Methods

¹²⁵I-porcine galanin (2200 Ci/mmol) was purchased from DuPont-NEN(Boston, Mass.). Various PCR/RACE oligonucleotide primers were customsynthesized by BRL Life Technologies (Grand Island, N.Y.). MARATHON RACEcDNA was obtained from Clontech, Palo Alto, Calif. Rat galanin and C7[Brain Research 600:268-272 (1993)] were purchased from PeninsulaLaboratories (Belmont, Calif.). Rat galanin 92-29) and rat galanin(3-29)were custom synthesized by Bio-synthesis, Inc.

Cloning vector pCR®2.1 and expression vector pCR®3.1 were obtained fromInvitrogen, San Diego, Calif. and used according to the manufacturer'sinstructions. TA cloning was carried out using pCR®2.1, whereby PCRproducts were ligated into the prepared vector without prior restrictioncleavage. Expression vector pCR®3.1 containing cDNA encoding themammalian GalR3 receptors was used to transfect COS cells. Human braincDNA and human genomic DNA were from Clontech and Premega, respectively.

Standard methods were used, as described, e.g., in Maniatis et al.,Molecular Cloning: A Laboratory Manual, 1982, Cold Spring HarborLaboratory, Cold Spring Harbor Press; Sambrook et al. Molecular Cloning:A Laboratory Manual, (2d ed.), Vols 1-3, 1989, Cold Spring Harbor Press,NY; Ausubel et al., Biology, Greene Publishing Associates, Brooklyn,N.Y.; or Ausubel, et al. (1987 and Supplements), Current Protocols inMolecular Biology, Greene/Wiley, New York; Innis et al. (eds.) PCRProtocols: A Guide to Methods and Applications, 1990, Academic Press,N.Y.

The polymerase chain reaction (PCR) and rapid amplification of cDNA ends(RACE) were carried out using the Clontech protocols. Briefly, PCR wasalways run with KLENTAQ polymerase, which possesses proof readingactivity (Clontech), and a cycling profile of 94° C. for 1 minute, 65°C. for 1 minute and 72° C. for 2 minutes (40 cycles). Approximately 1 μlof overnight E. coli cell culture was used in the PCR for sib selection.

For RACE, nested primers specific to the rat or human GalR3 cDNA andnested adaptor primers were used in the primary and secondary PCRs withabout 0.1 μg of genomic or cDNA as a template. Thermal cycling at 94° C.for 30 seconds, 65° C. for 30 seconds and 72° C. for 90 seconds (25cycles) was used in primary PCR. Cycling at 94° C. for 1 minute and 70°C. for 4 minutes (30 cycles) using 5 μl of the primary PCR product(diluted 1:50) as a template was used in the secondary PCR. A GC meltreagent (Clontech) at recommended dilution was always used in both PCRand RACE reactions.

DNA sequencing was performed with ABI Prism dye termination DNAsequencing reagents and an ABI automated sequencing apparatus (PerkinElmer, Branchburg, N.J.) or manually with a SEQUITHERM ECCEL sequencingkit (Epicentre Technologies, Madison, Wis.). DNA and protein sequencecomparisons were performed with DNA* software from DNAstar Inc.,Madison, Wis.

A rat hypothalamus cDNA library was constructed by standard methods.Briefly, total RNA from rat hypothalamus was extracted withTri-reagent-RNA/DNA/protein Isolation Reagent (Molecular ResearchCenter, Cincinnati, Ohio. Poly(A)⁺ RNA from the total RNA was purifiedwith an mRNA purification kit employing oligo(dT)-cellulosechromatography (Pharmacia, Piscataway, N.J.). Double-stranded cDNA wassynthesized from the poly(A)⁺ RNA with a Marathon cDNA amplification kit(Clontech). A portion of the cDNA was blunt-end ligated with an adaptorcontaining a BstXI restriction site. The BstXI adaptor-linked cDNA wasthen ligated into a pcDNA3 vector predigested with BstXI.

Transfection was carried out as follows. Confluent COS-7 cells (ATCC CRL1651) grown in DMEM supplemented with 10% fetal calf serum (FCS) with100 units/ml penicillin and 100 μg/ml streptomycin were split 1:6 into150 mm dishes (Nunc) three days prior to transfection. On the day oftransfection, the cells were approximately 90% confluent and trypsinizedoff plates and washed two times with PBS without Mg⁺⁺ and Ca⁺⁺. Thecells were resuspended in Krebs Ringer's buffer at a density ofapproximately 1.2×10⁷ cells/ml. Twenty μg of vector pCR®3.1 containingrat GalR3 cDNA was diluted in Krebs Ringer's buffer (100 μl finalvolume), mixed with 0.7 ml of the COS-7 cells in a 0.4 cmelectroporation cuvettes (Bio-rad, Hercules, Calif.) then chilled on icefor 5 min. The cells were electroporated at 960 μF×260 volts (timeconstant approximately 18) followed by incubation on ice for 10 min. Thecells were incubated in DMEM with 10% FCS in a 150-mm plate.

Methods utilizing the Lipofectamine reagents (BRL Life Technologies) andthe SuperFect reagents (Qiagene Inc., Chatsworth, Calif.) to transfectCOS-7 cells worked equally well.

Example 1 Cloning and Characterization of the Rat GalR3Receptor

In a BLAST [Altschul et al., J. Mol. Biol. 215:403-410 (1990)] search ofthe GenBank data base with the human GalR1 receptor amino acid sequence(Habert-Ortoli et al., supra) as a query sequence, a portion of a clonehaving Accession No. Z82241 was found to possess high homology with thehuman GalR1 sequence. The clone, identified as J81I2, is a human genomicsequence partially sequenced and arranged in the database as 31 segmentsseparated by thirty 800-n sequences in random order. Amino acid residues64-132 of the human GalR1 receptor aligned with an amino acid sequencetranslated at the third reading frame on the positive strand of cloneJ81I2 with 55% identity. A smaller homologous match between amino acidresidues 37-62 of the human GalR1 sequence and part of the translatednucleotide sequence of clone J81I2 (third reading frame on the positivestrand) was also found to be 57% identical in the same analysis.

The homology level (55-57%) found with this clone is significantlyhigher than a 40% homology found between the GalR1 and GalR2 receptors,and markedly lower than those between the species homologues of GalR1receptors among human, rat and mouse (>90%). Thus, part of thenucleotide sequence of clone J81I2 appeared to encode an amino acidsequence, corresponding to amino acid residues 37-132 of human GalR1, ofa new human galanin receptor designated the human GalR3 receptor.

In brief, the strategy used to obtain cDNA encoding the rat GalR3receptor was to generate several pairs of PCR primers, based on thehuman genomic clone, and to use them in RT-PCR with rat hypothalamus RNAas template to obtain a cDNA sequence of the GalR3 cDNA.

Two PCR primers, designated oligo93C (SEQ ID NO: 5) and oligo120B (SEQID NO: 6), produced a PCR product of approximately 700 bp which wascloned into vector pCR®3.1. The DNA sequence of the clone was comparedwith the nucleotide sequences in GenBank and the search resultsrevealed, in rank order, the human genomic clone (Z82241), rGalR2, andhGalR1 as the most homologous sequences, with identities of 86%, 65% and63%, respectively. The rat clone thus appeared to be the species homologof the putative human GalR3 cDNA.

To extend the cDNA sequence toward the 5′, and 3′ directions, RACE andPCR sib selection were used. In RACE amplification, primers designatedoligo 172 (SEQ ID NO: 7) and AP1 (SEQ ID NO: 8; outer adaptor primer)were used in the primary PCR and others designated oligo177 (SEQ ID NO:9) and AP2 (SEQ ID NO: 10; inner adaptor primer) were used in thesecondary PCR. The final RACE product, ≈1.8 kb, contained part of the 5′end of rat GalR3 cDNA and the upstream 5′ untranslated region.

In PCR sib selection, two primers designated oligo164 (SEQ ID NO: 11)and oligo167 (SEQ ID NO: 12) were used to screen a cDNA libraryconstructed from rat hypothalamus. The library was pooled at a size of≈5000 clones/pool, and DNA was prepared for each of the individualpools. A pool designated A28 gave a positive band amplified with the twoprimers and was sub-divided and screened until a single clone wasobtained. That clone, designated A28-1, was 1.3 kb long and possessedmost of the putative rat GalR3 cDNA.

A full-length rat GAlR3 cDNA clone was obtained by performing furthersib selection on the rat hypothalamus cDNA library using primer oligo185 (SEQ ID NO: 13), based on the sequence of the 5′ RACE product, andprimer oligo 184 (SEQ ID NO: 14), based on the sequence of clone A28-1.A single clone A5-3 selected from library pool A5 was obtained andsequenced. That clone was 2.2 kb long and contained all of the sequenceof clone A28-1 and part of the 5′ RACE product. A complete open readingframe (ORF) was identified in the clone, and the deduced amino acidsequence of the ORF consisted of 370 amino acids with a calculatedmolecular mass of 40.3 kDa.

Hydropathy analysis and comparison with other GalR receptors revealedseven putative transmembrane spanning domains (TMs) typical of G-proteincoupled receptors. The GalR3 receptor also contains a single potentialN-linked glycosylation site in the N-terminal region, two Cys residuesin the first and second extracellular loops that form a putativedisulfide bond in these receptors, and two Cys residues in theC-terminal region that may be involved in palmitoylation.

Example 2 Cloning and Characterization of the Human GalR3Receptor

To obtain the cDNA of the human GalR3 receptor, primers designated oligo93 (SEQ ID NO: 15) and oligo 94 (SEQ ID NO: 16) based on the human GalR3nucleotide sequence (Z82241) were used in PCR to generate the fragmentwith cDNA prepared by reverse-transcription of human brain cDNA(Clontech; 0.1 μg) and human placenta genomic DNA (Premega; 0.1 μg) astemplate. A single band PCR product of ≈300 bp in length, as analyzedwith agarose gel electrophoresis, was generated in both PCR reactions.The PCR product obtained with genomic DNA as template was cloned intothe pCR®2.1 vector to produce a clone designated pCR2.1-f93/94, andsequencing analysis showed that the cloned fragment was identical topart of the putative GalR3 sequence in genomic clone J81I2.

A series of nested forward and reverse primers within this sequence andhuman brain cDNA linked with adapters at the two ends was then used inRACE PCR to obtain the upstream and downstream cDNA sequences coveringthe start and stop codons. A 5′-RACE product, 0.5 kb long, was obtainedwith oligo 134 (SEQ ID NO: 17) and oligo 135 (SEQ ID NO: 18) as thenested GalR3-specific primers and the two adaptor-specific primers AP1(SEQ ID NO: 8) and AP2 (SEQ ID NO: 10). Similarly, an 1-kb 3′-RACEproduct was obtained with oligo 93B (SEQ ID NO: 19) and oligo 93C (SEQID NO: 5) as the nested GalR3-specific primers. Sequencing of these twofragments revealed an in-frame start codon in the 5′-RACE product and anin-frame stop codon in the 3′-RACE product.

The full length cDNA of the GalR3 receptor was obtained by PCR usinghuman brain cDNA as template and primers designated oligo 154 (SEQ IDNO: 20) and oligo 159A (SEQ ID NO: 21) to produce the long form, andprimers designated oligo 156 (SEQ ID NO: 22) and oligo 159A (SEQ ID NO:21) to produce the short form of the human GalR3 receptor.

Example 3 Agonist/Antagonist Screening Assay

Receptor membranes were prepared as follows. COS-7 cells transfected asdescribed above with vector pCR®3.1 containing cDNA encoding the ratGalR3 receptor were incubated in DMEM with 10% FCS in 150 mm plates for3 days in a humidified 5% CO₂ incubator, after which the medium wasremoved and the cells were washed three times with phosphate bufferedsaline (PBS).

To each plate, 5 ml of 5 mM Hepes buffer (pH 7.4), 0.1 mM PMSF, and 0.1mg/ml bacitracin were added and incubated at room temperature for 15minutes. The cells were scraped from the plates and centrifuged at13,000×g for 15 minutes at 4° C. The resulting cell pellet wasresuspended in 2 ml of 25 mM Tris-Cl (pH7.4) containing 0.2 mM PMSF byvortexing, and dispersed with a syringe attached with a #23 gaugeneedle. Protein concentrations were determined using a BCA(bicinchoninic acid) method (Pierce, Rockford, Ill.).

Binding of ¹²⁵I-porcine-galanin to the membrane preparations wasperformed in a buffer containing 25 mM Tris-Cl (pH7.4), 1% bovine serumalbumin (w/v), 0.1% bacitracin, 2 μg/ml leupeptin and 10 mM MgCl₂.Ligand saturation plots were performed using 20 μg amounts of themembrane protein in a total volume of 200 μl using 3 μM cold galanin todetermine nonspecific binding. Peptide competition studies wereperformed in a total volume of 200 μl, containing 20 μg of membraneprotein and 0.3 nM ¹²⁵I-porcine galanin. Incubations were carried out atroom temperature for 1 hour and were terminated by rapid vacuumfiltration through MULTISCREEN FB (glass fiber B) Filter Plates(Millipore, Bedford, Mass.) which had been pre-treated with 0.30%polyethylenimine to prevent non-specific binding of the radioligand tothe filter. The filters were then washed three times with 100 μl of PBS(pH7.4). All data were analyzed using non-linear regression software(Prism, GraphPad, San Diego, Calif.), and the Ki was calculated usingthe method of Cheng and Prusoff [Biochem. Pharmacol. 22:3099-3108(1973)].

In a typical assay, the results of which are shown in FIG. 2, thecompeting ligands rat galanin (), chimeric galanin peptide C7 (◯),galanin(2-29) (□), galanin(3-29) (•) and galanin(10-20) (▴) produced Kivalues of 1.2, 1.4, 14, >1,000 and >1,000 nM, respectively. The curvesshown indicate the fits of the data points by nonlinear regression forone-site binding.

As shown in FIG. 2, compounds known to have galanin activity, i.e.,galanin itself, galanin peptide C7 and galanin(2-29), were allcompetitive inhibitors of the labeled galanin, whereas the compoundslacking galanin activity, i.e., galanin(3-29) and galanin(10-20), werenot. Thus, the assay has a high degree of ligand specificity and shouldbe generally applicable to the identification of galanin agonists andantagonists.

Many modifications and variations of this invention can be made withoutdeparting from its spirit and scope, as will be apparent to thoseskilled in the art. The specific embodiments described herein areoffered by way of example only, and the invention is to be limited onlyby the terms of the appended claims, together with the full scope ofequivalents to which such claims are entitled.

1. An isolated mammalian galanin receptor comprising an amino acidsequence defined by SEQ ID NO: 2 or SEQ ID NO: 4, or a conservative orallelic variant thereof.
 2. An antibody which specifically binds to themammalian receptor of claim
 1. 3. The antibody of claim 2 which is amonoclonal antibody.
 4. An anti-idiotypic antibody produced against theantibody of claim
 2. 5. The antibody of claim 4 which is a monoclonalantibody.
 6. An isolated or recombinant nucleic acid encoding themammalian galanin receptor of claim
 1. 7. A recombinant vectorcomprising the nucleic acid of claim
 6. 8. A host cell comprising therecombinant vector of claim
 7. 9. A method for making a mammaliangalanin receptor comprising culturing a host cell of claim 8 underconditions in which the nucleic acid is expressed.
 10. The method ofclaim 9 in which the receptor is isolated from the culture.
 11. Anisolated or recombinant nucleic acid selected from the group consistingof: (a) a nucleic acid encoding a mammalian galanin receptor comprisingan amino acid sequence defined by SEQ ID NO: 2 or SEQ ID NO: 4, or asubsequence thereof; (b) a nucleic acid that hybridizes under moderatelystringent conditions to the nucleic acid of (a) and encodes apolypeptide that (i) binds galanin and (ii) is at least 80% identical toa receptor encoded by the nucleic acid of (a); and (c) a nucleic acidthat, due to the degeneracy of the genetic code, encodes a mammaliangalanin receptor encoded by a nucleic acid of (a) or (b).
 12. Arecombinant vector comprising the nucleic acid of claim
 11. 13. A hostcell comprising the recombinant vector of claim
 12. 14. A method formaking a mammalian galanin receptor comprising culturing a host cell ofclaim 13 under conditions in which the nucleic acid is expressed. 15.The method of claim 7 in which the receptor is isolated from theculture.
 16. A method for identifying a galanin receptor agonist orantagonist comprising: (a) contacting a polypeptide comprising an aminoacid sequence set forth in SEQ ID NO: 2, SEQ ID NO: 4 or amino acids57-424 of SEQ ID NO: 4 in the presence of a known amount of labeledgalanin ligand with a sample to be tested for the presence of a galaninreceptor agonist or antagonist; and (b) measuring an amount of labeledgalanin ligand specifically bound to the polypeptide; whereby a galaninagonist or antagonist in the sample is identified by measuringsubstantially reduced binding of the labeled galanin ligand to thepolypeptide, compared to that measured in the absence of such agonist orantagonist.
 17. The method of claim 16 wherein the labeled galaninligand is ¹²⁵I-galanin.
 18. The method of claim 16 further comprisingthe following steps: (c) contacting a mammalian GalR1 or GalR2 receptorin the presence of a known amount of labeled galanin with a compoundidentified as a galanin agonist or antagonist in steps (a) and (b); and(d) measuring the amount of labeled galanin bound to the receptor;whereby a galanin agonist or antagonist specific for the GalR3 receptoris identified by measuring substantially undiminished binding of thelabeled galanin to the GalR1 or GalR2, compared to that measured in theabsence of such agonist or antagonist.
 19. The method of claim 16wherein the polypeptide is in a cell membrane.
 20. The method of claim16 wherein said galanin ligand is galanin, galanin peptide C7 or aminoacids 2-29 of galanin.
 21. A method for identifying a galanin receptorantagonist comprising: (a) contacting a polypeptide comprising aminoacids 57-424 of SEQ ID NO: 4 in the presence of a known amount of¹²⁵I-labeled galanin with a sample to be tested for the presence of agalanin antagonist; and (b) measuring an amount of ¹²⁵I-labeled galaninspecifically bound to the polypeptide; whereby a galanin antagonist inthe sample is identified by measuring substantially reduced binding ofthe ¹²⁵I-labeled galanin to the polypeptide, compared to that measuredin the absence of such antagonist.